JPS6055569B2 - Heating temperature control method for seamless steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating temperature control method for steel materials charged into a furnace, and particularly in a heating furnace for seamless steel pipes, when the dimensions and shape of the steel pipes or the extraction cycle time change. The present invention relates to a heating temperature determining method for determining the optimal heating time and furnace temperature setting, thereby preventing overheating of the steel pipe and saving energy.

In the production of seamless steel pipes, a billet is heated in a heating furnace to a predetermined temperature, and after performing primary and secondary drilling, it is heated again in a reheating furnace, and then cut to a predetermined outer diameter with a sizer. Finish.

In this heat treatment, if the heating temperature is inappropriate, it may cause deflection or flaws, so it is necessary to uniformly heat the steel at a temperature that provides the best workability for each type of steel. By the way, in the heating furnace or reheating furnace, generally a plurality of steel pieces or hollow materials are intermittently passed through a plurality of temperature zones and sequentially taken out from the extraction port. The time it takes for these pieces of steel to move intermittently within one furnace is called one cycle time. Generally, the heating time T of the cold shell in the reheating furnace is expressed by the following equation when the set temperature is the same.

T=to-m)m=d(D/d)/D However, d is the constant of proportionality, d is the wall thickness, and D is the outer diameter.

This calculation formula determines the in-furnace time of the reheating furnace, and determines the cycle time for one steel pipe.

However, this calculation formula can be applied to heating from a certain fixed temperature, but the charging temperature in the furnace is (a) shell outer diameter, (
口) If it changes depending on shell thickness and rolling cycle time, it must be determined separately. As a result of examining the change in charging temperature for the above (a) to ←→ by various measurements, it was found that there is a proportional relationship between the charging temperature into the furnace and the wall thickness of the shell. That is, the thicker the shell, the higher the heat retained by the shell and therefore the charging temperature, and the smaller the difference from the extraction temperature. In particular, when m exceeds a certain value, the heating time may actually be shortened. If this measurement result is illustrated, it will look like the solid line in FIG. Conventionally, the charging temperature was kept constant regardless of the shell thickness.
The heating time is increased linearly with respect to the increase in m.
In FIG. 1, it increases uniformly as shown by the chain line. That is, in the conventional method, thermal energy is wasted without taking into account changes in the shell charging temperature. Based on the above-mentioned experimental results, the present invention calculates a certain reduction rate with respect to the set temperature based on conventional theoretical calculations, and performs heat treatment at a lower temperature by this reduction rate, that is, with less energy, thereby shortening the extraction cycle time. The purpose is to save energy, and the relationship between the shell shape expressed by m above and the heating time is experimentally determined to achieve the optimal thermal efficiency.
The set temperature lapse rate is determined from the optimum heating time obtained using this relationship.

Then, the set temperature of the heating zone is controlled based on this set temperature lapse rate. That is, the heating temperature control method for seamless steel pipes according to the present invention is based on the relationship between the shell shape and heating time when the shell thickness, outer diameter, extraction cycle time, etc. change, and the heating zone is controlled by the following steps. This is to control the set temperature. (b) The process of determining the maximum heating time from the conditions under which cold shells are charged, (0) The heating time T that experimentally provides the optimum thermal efficiency by taking into account the heat retained in the shells to be charged.
The process of finding T=Km+c, where K: proportionality constant, c: experimentally determined constant, m=d(D-d)/D d: shell thickness, D: shell outer diameter, (c) the above A step of comparing the heating time that yields the optimum thermal efficiency with the maximum heating time determined in (a) above, and determining the set temperature lapse rate according to the excess; (d) determining the heating zone temperature based on the set temperature lapse rate. The process of controlling the set temperature.

In this way, the present invention focuses on the fact that the heat retained in the shell charged in the reheating furnace varies greatly depending on the shell thickness, and finely controls the set temperature of the heating zone and uses it for heating. As a result of adjusting the fuel, significant energy savings can be achieved.

Hereinafter, the present invention will be specifically described with reference to the drawings.

As shown in the experimental results in FIG. 1, the shell charging temperature increases linearly as the wall thickness increases, so the optimal heating time in terms of thermal efficiency becomes parallel to the horizontal axis when K=10 or more.

The relationship between optimal thermal efficiency in this example is expressed mathematically as follows:
V) Easy 1J1) Av●VS tool υVOVV~
'Exposure. When m≧10.8, T=-1.77m+39.7
2 If we compare the conventional case, at a certain value of m in the figure, a
You can save heating time by that amount.

Suppose that a certain number of m shells are loaded into the heating furnace. If this shell is sent through the furnace in one pocket at a cycle time of t (seconds), it is assumed that this shell passes through the heating furnace at t×(number of pockets)=T. In the previous example, the optimal furnace time at this time is b (seconds), and the excess of the conventional heating time is a.
(seconds). The relationship between a and the lapse rate of the heating zone temperature setting is illustrated in FIG. 2. As a specific example, the outer diameter is 360! ! r! 11. When a shell with a wall thickness of 10.0 WIR is charged into the furnace, m = 9.72, b = 330 (seconds)
In the case of 10 pockets, one cycle is 33 (seconds). On the other hand, when the cold shell is charged, the maximum cycle time determined from the maximum heating time shown by the chain line in Fig. 1 is, assuming that it is moved one pitch (pocket) at t = 55 (seconds), a = t x (number of pockets) - b = 220 (seconds), and in this case, the rate of decrease in the set temperature is 0 from Figure 2.
．． It becomes 947.

Therefore, for example, if the setting is 9000C, the temperature will be 900℃.
The set temperature is changed to ×0.947=8539C. FIG. 3 is a schematic side sectional view of an actual shell heating furnace. There are one shell 4 in the heating zone and eight shells in the soaking zone in the furnace casing 10, and a walking beam 2.
The figure shows the state in which it is carried in each pocket 9 and sequentially moves in the direction of the arrow.

The charging roller 3 detects the vibrator position and stops, and the motor 7
starts rotating. Beam frame 5 via cam 6
The walking beam 2 connected thereto rotates in the direction of the chain line and sends out the shells 4 one by one to the conveying roller 1. A limit switch 8 installed under the hearth controls the time from the completion of this delivery to the completion of delivery of the next material.
is detected, and the time in between is measured and defined as one cycle time. The theoretical cycle time of this shell is (heating time)/2 from the heating time shown by the solid line in Figure 1.
Calculated as a pot. This theoretical cycle time and the aforementioned cycle time t (seconds) are compared to determine the set temperature in the heating zone. Since the calculation of the above-mentioned excess time a is performed for each loaded shell, the heating furnace set temperature changes every moment.

In this case, the following conditions are adopted to prevent too sudden changes. (a) Limits on the minimum value of furnace temperature (1) Within the same lot, the theoretical cycle time should be adjusted to the longest one.

For example, assume that the furnace temperature width is 1 (generation). (c) Human intervention during long-term outages.

According to the present invention, the temperature setting of the heating furnace can be set to the most efficient temperature in terms of energy saving based on the shell thickness, outer diameter, etc., and the optimum furnace life time of the shell.

This will prevent overheating of the vibrator, shorten cycle time, and is expected to save energy by nearly 10% depending on rolling conditions.

[Brief explanation of drawings]

Figure 1 shows the relationship between the shell shape m and heating time at optimum thermal efficiency, Figure 2 shows the relationship between the set temperature lapse rate and the heating time excess a, and Figure 3 shows the relationship between the shell shape m and the heating time at the optimum thermal efficiency. FIG. 2 is a schematic side sectional view showing an example of an applied heating furnace. 1... Conveyance roller, 2... Walking beam, 3... Charging roller, 4...
Shell, 9...pocket, 10...furnace casing.

Claims (1)

[Claims] 1. Based on the relationship between shell shape and heating time when shell thickness, outer diameter, extraction cycle time, etc. change,
A heating temperature control method for seamless steel pipe, characterized by controlling the set temperature of a heating zone through the following steps. (a) The process of determining the maximum heating time from the conditions under which cold shells are charged; (b) The process of determining the heating time T that gives the optimum thermal efficiency experimentally by taking into account the heat retained in the shells to be charged. =
Process determined as Km+c, where K: proportionality constant, c: constant determined experimentally, m=d(D-d)/D d: shell thickness, D: shell outer diameter, (c) the above-mentioned optimum thermal efficiency and A step of comparing the heating time obtained in the above (a) with the maximum heating time obtained in the above (a) and determining a set temperature lapse rate according to the excess, (d) setting the set temperature of the heating zone based on the above set temperature lapse rate. Process to control.